Installation Testing Maintenance Instructions
INSTALLATION INSTRUCTIONS
CAUTION: Installation of Backow Preventers must be performed by qualied, licensed
personnel. The installer should be sure the proper device has been selected for the par-
ticular installation. Faulty installation could result in an improperly functioning device.
ZURN WILKINS Model 375AST Series Reduced Pressure Principle assemblies are for use
on potable water lines where a health hazard exists in the event of a backow situation.
Damage to the device could result wherever water hammer and/or water thermal ex-
pansion could create excessive line pressure. Where this could occur, shock arrestors,
check valves and/or pressure relief valves should be installed downstream of the device.
If installation is in a pit or vault, the Backow Preventer must never be submerged in
water because this could cause a cross-connection. Make sure that the pit or vault always
remains dry by providing ample drainage. (Consult local codes.)
1. Before installing a Model 375AST Series Backow Preventer, ush the line thoroughly
to remove all debris, chips and other foreign matter. If required, a strainer should
be placed upstream of the Backow Preventer. CAUTION: Do not use a strainer
in seldom used emergency waterlines such as re lines.
2. Provide adequate space around the installed unit so that the test cocks will be ac-
cessible for testing and servicing.
3. Install valve at least 12 inches above surrounding ood level.
4. Always consult local codes for installation methods, approvals and guidance.
5. Resilient seated shutoff valves are required to be installed on both the inlet and
outlet of the device to make eld testing possible.
6. The Model 375 series has been tested and approved in the horizontal position.
Contact Factory before installing in other orientations.
INDOOR INSTALLATION
Indoor installation is preferred in areas that
are subject to freezing conditions. All the
basic installation instructions apply to such
installations. CAUTION: An adequately
sized drain is required to prevent pos-
sible water damage due to relief valve
discharge.
OUTDOOR INSTALLATION
The Model 375AST Series Backow Pre-
venter may be installed outdoors only if the
device is protected against freezing condi-
tions. Exposure to freezing conditions will
result in improper function or damage to the
device. The installation location must be
kept above 32°F. All the basic installation
instructions apply.
PLACING THE MODEL 375AST IN SERVICE
1. Start with both shut-off valves
closed. Slowly open the inlet shut-off
valve until the Backow Preventer
is completely pressurized. A brief
discharge from the relief valve may
occur while the device is pressurizing.
The discharge should cease by the
time the shut-off valve is fully open. If
the discharge does not stop, refer to
"MAINTENANCE INSTRUCTIONS" for
repair procedures.
2. After the device has been pressurized,
vent all trapped air by slightly opening
each of the four test cocks.
3. Slowly open the downstream shut-
off valve. The Model 375AST Series
Reduced Pressure Principle Backow
Preventer is now in service.
4. If spitting or intermittent discharges
from the relief valve are noted, it
could be a result of pressure uctua-
tion and/or a water hammer condition
in the system. If such conditions exist,
install water pressure reducing valves
or water hammer shock arrestors in
compliance with industry standards as
needed.
5. After the Model 375AST has been
properly installed, test the device (see
"TEST PROCEDURES"). If the device
fails the test, remove the rst and
second check valves and thoroughly
ush the device. If the relief valve fails
to operate properly, inspect the sens-
ing passage for clogging (see "MAIN-
TENANCE INSTRUCTIONS"). Clean
rubber seals of all debris and place
unit back in service.
Model 375AST(R) & 375ASTDA(R)
Reduced Pressure Principle Assembly (Size 8" & 10") and
Reduced Pressure Detector Assembly (Size 8" & 10")
OUTDOOR INSTALLATION
MODEL 375ASTBG
12" MIN.
30" MAX.
DIRECTION OF FLOW
DIRECTION OF FLOW
12" MIN.
30" MAX.
DIRECTION OF FLOW
12" MIN.
30" MAX.
®
LEAD-FREE*
*This product contains a weighted average lead content less than 0.25% for wetted surfaces.
(Patent No. 8,997,772)
! WARNING: Cancer and Reproductive Harm - www.P65Warnings.ca.gov
! ADVERTENCIA: Cáncer y daño reproductivo - www.P65Warnings.ca.gov
! AVERTISSEMENT: Cancer et néfastes sur la reproduction - www.P65Warnings.ca.gov
Testing Procedures
2
ZURN WILKINS
1747 Commerce Way, Paso Robles, CA 93446 Phone:855-663-9876 Fax:805-238-5766
3. Open the vent needle valve. If the indicated differential
pressure reading remains steady then the #2 check valve
is reported as "closed tight." Go to Test #3. If the differential
pressure reading falls to the relief valve opening point, bleed
water through the low side bleed needle valve until the
gauge reading reaches a value above the #1 check valve
pressure drop. If the gauge reading settles above the relief
valve opening point, record the #2 check valve as "closed
tight," and proceed to Test #3. If the differential pressure
reading falls to the relief valve opening point again, then
the#2 check valve is noted as "leaking," and Test #3 cannot
be completed. If the differential pressure reading drops, but
stabilizes above the relief valve opening point, the #2 check
valve can still be reported as "closed tight."
Note: Due to disc compression, you may need to bleed off
before the gauge reading will settle above relief valve opening
point.
TEST NO.3 - TIGHTNESS OF #1 CHECK VALVE
REQUIREMENT:
The static pressure drop across #1 check valve shall be greater
than the relief valve opening point (test #1), and at least 5.0 psid.
PROCEDURE:
1. With the vent hose connected to test cock #4 as in step 3
of Test #2, bleed water from the zone through the low side
bleed needle valve on the gauge until the reading exceeds
the #1 check valve pressure drop. Close the low side bleed
needle valve. After the gauge reading settles, the steady
state differential pressure reading indicated (reading is not
falling on the gauge) is the actual static (i.e., no ow) pres-
sure drop across check valve #1 and is to be recorded as
such.
2. Close all test cocks, slowly open shutoff valve #2 and remove
equipment.
#2 SHUTOFF VALVE
#1 SHUTOFF VALVE
#1 TEST COCK
#2 TEST COCK
#4 TEST COCK
LOW SIDE BLEED
NEEDLE VALVE (GREEN)
LOW SIDE HOSE
(GREEN)
HIGH SIDE BLEED
NEEDLE VALVE (RED)
HIGH SIDE HOSE
(RED)
VENT HOSE
(BLACK)
#3 TEST COCK
®
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MODEL 375AST REDUCED PRESSURE ASSEMBLY
Equipment Required: Differential pressure gauge test kit.
TEST NO. 1 - RELIEF VALVE OPENING POINT
REQUIREMENT:
The differential pressure relief valve must operate to maintain the
zone between the two check valves at least 2 psi less than the
supply pressure.
PROCEDURE:
1. Flush water through test cocks #1, #2 (open #2 slowly), #3
and #4 by opening and closing each test cock one at a time,
to eliminate foreign material.
2. Install appropriate ttings to test cocks. Attach hose from the
high side of the differential pressure gauge to the #2 test
cock then attach hose from the low side of the gauge to the
#3 test cock. Open test cock #3 slowly and then bleed all
air from the hose and gauge by opening the low side bleed
needle valve.
3. Maintain the low side bleed needle valve in the open position
while test cock #2 is opened slowly. Open the high side bleed
needle valve to bleed all air from the hose and gauge. Close
the high side bleed needle valve, then close the low side
bleed needle valve after the gauge reading has reached the
upper end of the scale.
4. Close the #2 shut-off valve. If the gauge reading drops to
the low end of the gauge scale and the differential pressure
relief valve discharges continuously, then the #1 check valve
is leaking. If this occurs, Tests #1, #2 and #3 cannot be com-
pleted (See USC Maintenance Guide). However, should the
gauge reading remain above the differential pressure relief
valve opening point, then observe the gauge reading. This is
the apparent pressure drop across the #1 check valve.
5. Open the high side control needle valve approximately one
turn, and then open the low side control needle valve no
more than 1/4 turn to by-pass water from the #2 test cock to
the #3 test cock. Observe the differential pressure reading
as it slowly drops to the relief valve opening point. Record
this opening point value when the rst discharge of water is
detected. Close the low side needle valve.
TEST NO. 2 - TIGHTNESS OF #2 CHECK VALVE
REQUIREMENT:
The #2 check valve shall be tight against backpressure.
PROCEDURE:
1. Maintain the #2 shut-off valve in the closed position (from
Test #1). Vent all air through the vent hose by opening the
vent needle valve. Close the vent needle valve only (The
high side control needle valve is to remain open.).
2. Attach the vent hose from the gauge to the #4 test cock,
then open the #4 test cock. Bleed water from the zone by
opening the low side bleed needle valve on the gauge
order to re-establish the normal reduced pressure within the
zone. Once the gauge reading reaches a value above the #1
check valve pressure drop, close the low side bleed needle
valve.
Maintenance Instructions
3
RELIEF VALVE ASSEMBLY
SEAT ASSEMBLY
SEAL RING
O-RING
(BOLT)
RETAINER
WASHER
BOLT
All Model 375AST Reduced Pressure Principle Backow Preven-
ters must be inspected and maintained by licensed personnel at
least once a year or more frequently as specied by local codes.
Replacement of worn or damaged parts must only be made with
genuine "ZURN WILKINS" parts.
GENERAL MAINTENANCE
1. Clean all parts thoroughly with water after disassembly.
2. Carefully inspect rubber seal rings and o-rings for damage.
3. Test unit after reassembly for proper operation (refer to
"TESTING PROCEDURES").
SERVICING RELIEF VALVE
1. Remove relief valve cover bolts and cover. Gently pull on
diaphragm to remove the cartridge assembly.
2. Inspect seal ring for cuts and embedded debris. Turn over or
replace if required.
3. Disassemble cartridge by unscrewing relief valve retainer
4. Inspect diaphragm and o-rings for damage. Replace re-
quired parts and apply a light coat of lubricant to plunger
o-ring.
5. Carefully reassemble cartridge assembly.
6. Inspect relief valve seat for wear on seating surface. If dam-
aged, replace seat and seat o-ring. Install spring over seat
guides.
7. Insert cartridge assembly into relief valve body.
8. Replace relief valve cover and cover bolts.
9. Place the device in service and test per "TESTING PRO-
CEDURES" on page 2.
CHECK ASSEMBLY
COVER
BOLTS
COVER
UPPER
PLUNGER
DIAPHRAGM
PLUNGER
O-RING
LOWER
PLUNGER
SEAL
RING
WASHERS
RETAINER
SCREW
SEAT
SPRING
BODY
SEAT
O-RING
#1 CHECK ASSEMBLY
#2 CHECK ASSEMBLY
(8" - 10")
SERVICING CHECK VALVES
A ratchet wrench, 11/16" deep socket, and a 4" long extension
are recommended for removing check assemblies.
1. Close inlet and outlet shut-off valves.
2. Open No. 2, No. 3 and No. 4 test cocks to release pressure
from valve.
3. Loosen & remove the grooved coupling around the access
cover. Remove cover. Place towel or cardboard over relief
valve port in body to prevent parts from falling into relief
valve.
4. To service only the #1 check assembly, remove the 6 bolts,
washers and o-rings from the back of the #1 check assem-
bly. Separate the retainer and the seal ring from the check
assembly and proceed to step #8.
5. To service both checks or the #2 check, the #1 check
assembly must rst be removed. Remove the 4 nuts and
washers retaining the #1 check assembly. Remove the #1
check assembly from the body.
6. To remove the #2 check assembly, remove the 7 nuts,
washers and the #2 check retaining ring. Grasp the check
assembly by the stem and remove from valve.
7. Remove all 6 bolts, washers and o-rings from the check
assembly (See "Check Assembly" illustration). Separate
retainer from check assembly to expose seal ring for inspec-
tion.
8. Inspect the rubber seal ring for cuts or embedded debris. If
the reverse side of the seal ring is unused, it is possible to
invert the seal ring. This would be considered a temporary
solution to xing a fouled check and should be replaced with
a new seal ring as soon as possible.
9. Inspect valve cavity and seating areas. Remove any debris.
10. Reverse the above procedures to reinstall check assem-
blies. Lubricate seat o-rings to hold them in place while
reinstalling seat. Place washers on studs and tighten retain-
ing nuts evenly.
11. Remove towel or cardboard covering from relief valve port.
Reinstall access cover and grooved coupling.
NOTE: If any portion of the seat assembly is damaged or missing
or if the seat sealing rib is damaged in any way, do not attempt to
eld repair it. Contact your local ZURN WILKINS representative for
assistance.
⃟
Rated Flow (Established by approval agencies)
0
69
138
207
0.0 63.1 126.2 189.3 252.4
0
10
20
30
0 1000
2000 3000
4000
PRESSURE LOSS (kPa)
FLOW RATES (l/s)
PRESSURE LOSS (PSID)
FLOW RATE (GPM)
MODEL 375ASTDA 6", 8" & 10" (STANDARD AND METRIC)
0
69
138
207
0.0 63.1 126.1 189.2 252.3
0
10
20
30
0 1000 2000 3000 4000
PRESSURE LOSS (kPa)
FLOW RATE (l/s)
PRESSURE LOSS (PSID)
FLOW RATE (GPM)
MODEL 375AST 8" & 10" (STANDARD AND METRIC)
ZURN WILKINS
1747 Commerce Way, Paso Robles, CA 93446 Phone:855-663-9876 Fax:805-238-5766
IS375AST-8 (REV. E 6/17)
4
Performance Characteristics
Troubleshooting
Proper performance is dependent upon licensed, qualied personnel performing regular, periodic testing according to ZURN WILKINS' specications
and prevailing governmental & industry standards and codes and upon following these installation instructions. Failure to do so releases ZURN
WILKINS of any liability that it might otherwise have with respect to that device. Such failure could also result in an improperly functioning device.
SPECIFICATIONS
Maximum working water pressure: 175 PSI
Maximum working water temperature: 140°F
Hydrostatic test pressure: 350 PSI
End connections: Flanged ANSI B16.1 Class 125
End connections: Grooved AWWA C606 - Steel
Repair Kits
SIZE MODEL 375AST RELIEF RUBBER ONLY MODEL 375AST RELIEF COMPLETE MODEL 375AST CHECKS ONLY
8" RK8-375R RK8-375 RK8-350
10" RK8-375R RK8-375 RK8-350
PROBLEM POSSIBLE CAUSES CORRECTIVE ACTION
1. SUDDEN OR RAPID 1. Drop in inlet pressure. 1. Install an in-line spring loaded check valve or pressure reducing
SPITTING 2. Sudden increase in downstream valve upstream of Backow Preventer.
pressure due to waterhammer 2. Install an in-line spring loaded check valve or pressure reducing
from quick closing shut-off valve valve downstream of Backow Preventer.
installed downstream.
2. LIGHT INTERMITTENT 1. Slightly fouled #1 check. 1. Clean #1 check and/or turn check valve seal ring over or replace.
DRIP 2. Slightly fouled relief valve seat. 2. Clean relief valve seat and/or turn relief valve seal ring over or
replace.
3. CONTINUOS 1. Fouled #1 check and/or #2 check. 1. Clean check valves and/or turn check valve seal ring over or
DISCHARGE 2. Fouled relief valve seat. replace.
2. Clean relief valve seat and/or turn relief valve seal ring over or
replace.
Capacity thru Schedule 40 Pipe
Pipe size 5 ft/sec 7.5 ft/sec 10 ft/sec 15 ft/sec
2 1/2" 75 112 149 224
3" 115 173 230 346
4" 198 298 397 595
6" 450 675 900 1351
8" 780 1169 1559 2339
10" 1229 1843 2458 3687
12" 1763 2644 3525 5288
8" (200mm)
10" (250mm)
8" (200mm)
10" (250mm)
®
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/